1. Field of the Invention
The present invention relates to a semiconductor laser, in particular, to a semiconductor laser with a wave band of 1 .mu.m suitable for exciting an optical fiber amplifier.
2. Relative Background Art
In such a semiconductor laser, InP is used for a substrate thereof. A mesa shape region that guides rays of light is formed in an active layer formed by epitaxial growth method. Both side portions of the mesa shape region are buried by high resistance semiconductor. Thus, current and rays of light are confined in the mesa shape region. This construction is known as buried type construction. For a semiconductor laser that has a substrate composed of GaAs, however, it was difficult to accomplish the buried type construction. Though, very recently, a buried type GaAs substrate semiconductor laser with a GaInP cladding was proposed, it will take a long time to place it in the market since the semiconductor laser does not provide high reliability. Accordingly, in a semiconductor laser using a GaAs substrate, a current block layer is formed on an active layer expect a current passage region, that is a center of the active region, without the active layer formed by epitaxial growth method is etched out.
However, in this construction, since the difference of equivalent refractive indexes in horizontal direction cannot be increased, rays of light tend to diffuse in the horizontal direction, thereby decreasing the radiation angle in the horizontal direction. Consequently, the ratio between the radiation angle in a vertical direction and the radiation angle in the horizontal direction becomes large. This ratio is referred to as aspect ratio. As a result, it is difficult to reduce the loss of the connection of the semiconductor laser against an optical fiber cable or the like.